The Assignee of the present invention, M&M Precision Systems Corporation, has commercialized prior monitoring systems for determining or confirming the shape of a machined item such as a gear and the like. These prior art monitoring systems are commercially sold under the designation Model Numbers 3012, 3018, 3025, 3040 and 3060 where the last two digits indicate the diameter of the workpieces (in inches) the system is capable of monitoring.
The prior art systems sold by the Assignee of the invention include a moveable frame mounted to a base and including a drive system for moving a stylus or probe along three independent directions by controlled energization of multiple drive motors. As an example, the frame could be moved horizontally in the direction of a first axis by means of a motor that rotates a precision ground ballscrew. As the ballscrew rotates the frame is moved very accurately with respect to an origin.
The carriage supports an arm extending away from the frame having a stylus at one end which comes into contact with the object under examination. The stylus is constructed using an LVDT monitoring probe. Such a probe produces an output signal related to the position of a moveable probe member with respect to the probe body. Through a controlled monitoring of the output signals from the probe, and controlled continuous movement of the frame, including a feedback monitoring of optical encoder signals as the frame moves, the monitoring system can accurately determine the position of the moveable probe tip. This allows the monitoring system to accurately compare any curve on a surface of a machined part with the desired shape of that surface. Alternately the monitoring system can test an unknown surface and store a representation of the part for late use as a standard.
In accordance with the prior art monitoring systems, the object under examination is supported on a turntable and held in place by a clamping member having a live center which is motor actuated. The object under examination is placed on the turntable and the clamp energized to bring the object engaging portion of the damp into engagement with the object. Once the object has been secured to the turntable, controlled energization of a turntable drive causes the object to rotate. Precise control over the turntable rotation is achieved by means of an air bearing which supports the turntable above a turntable support and feedback monitoring of sensed turntable rotation.
The combination of extremely accurate rotation of the object under examination, in conjunction with the use of a ballscrew drive for moving the carriage has added to the cost of making prior art monitoring systems. Accurate movement and position sensing require the frame that supports the probe to be leveled both during manufacture of the monitoring system and as it is installed. This is achieved in the prior art by scraping engagement surfaces of the carriage support during fabrication of the monitoring system. This scraping process is done manually and performed on a trial-and-error basis. A significant amount of time during production of a monitoring system goes into the scraping and leveling of the moveable carriage that supports the probe or stylus.
The prior art systems sold by M&M Precision Systems are expensive to build. It is one object of the present invention to provide an accurate yet economic monitoring system without resort to some of the more expensive components and techniques used in prior art monitoring systems.